Field of the Invention and Related Art Statement
The present invention relates to an optical head using an image sensor of XY address type in an optical information recording and playback apparatus for optically recording or playing back information.
An optical head which is used in an optical information recording and playback apparatus for optically recording or playing back information is arranged such that an optical beam generated from a light source is irradiated onto an optical recording medium, and at least a part of a beam reflected or transmitted through the optical recording medium is received by a photo detector, so that a focus error signal or a tracking error signal is generated for exact execution of recording and playback, or a signal for playing back the information on the optical recording medium is generated.
A prior art example of an optical head used in an apparatus for optically playing back information, in which a rectangular optical card serves as an optical recording medium will hereunder be described.
FIG. 1 of the attached drawings shows an arrangement of an optical system of an optical head which executes detection of a focus error of axis-missing type and detection of a tracking error of the three beam type. Solid lines In FIG. 1 show an optical axis of the beam, but do not show a beam configuration. The optical beam generated by a laser diode 1 is brought to a substantially an ellipse shaped parallel beam by a collimator lens 2.
The parallel beam is reduced along only the major-axis direction of the ellipse by a shaping prism 3, and is shaped substantially into a circle, and a diameter of the parallel beam is restricted by a circular iris or stop 4 such that the size of a spot on the optical recording medium (that is, an optical card 8) is brought to a predetermined value. The parallel beam is further divided into three optical beams including one beam comprised of zero-order diffracted light and two beams respectively comprising .+-. primary diffracted light by a diffraction grating 5, and these three beams are reflected by a mirror 6. Subsequently, the parallel beam is incident upon an objective lens 7 at a position which is eccentric with respect to the optical axles of the objective lens 7.
These three optical beams are condensed by the objective lens 7, and are irradiated onto the optical card 8 in which a plurality of tracks 12, 12, . . . are formed. Thus, the three optical beams are caused to form three circular spots, respectively, as shown in FIG. 2. Meanwhile, the three optical beams reflected from the optical card 8 pass through the objective lens 7 in an opposite direction so that they become substantially parallel light beams. The parallel light beams are reflected from the mirror 6 and, subsequently, are incident upon the condensing lens 9. These three beams are condensed onto a photo detector 10 by the condensing lens 9.
The photo detector of the optical head according to the prior art example is arranged as shown in FIG. 3(b) such that a light receiving surface is divided into elements which are arranged thereon. Upon focusing, the light receiving elements are so regulated as to be located at an appropriate position with respect to the optical beam such that the optical beam of the zero-order diffracted light is located at the center of a four-divided light receiving device 20 having four light receiving elements A, B, C and D, and two optical beams comprised of primary diffracted lights form spots at a center of a light receiving element 21 of E and at the center of a light receiving element 22 of F, respectively.
A method of detecting the focus error will be described with reference to FIG. 3a and FIG. 3b. The optical beam comprised of the zero-order diffracted light indicated as an optical axis 17 is reflected from the mirror 6, and is incident upon a position eccentric with respect to the optical axis of the objective lens 7, and is condensed onto the optical card 8. At this time, if the optical card 8 is located at the focusing position of the objective lens 7, the optical beam reflected from the optical card 8 becomes an optical beam designated as an optical axis 18. The optical beam is reflected by the mirror 6 and, subsequently, is condensed by the condensing lens 9, to form a spot at a position designated as 19 on the optical detector 10. Output signals from the four-divided light receiving device 20 then have the relationship of (A+B)-(C+D)=0.
On the other hand, if the optical card 8 is displaced in a direction indicated by an arrow a in FIG. 3(a) and is brought to a position spaced apart from the focus position of the objective lens 7, the optical beam reflected from the optical card 8 is brought to an optical beam designated as an optical axis 18a so as to form a faded spot having its center at a position designated as 19a on the photo detector 10. Output signals from the four-divided light receiving device 20 have the relationship of (A+B)-(C+D) &lt;0. Further, when the optical card 8 is displaced in the direction indicated by arrow b so as to be located at a position spaced away from the focus position of the objective lens 7, the optical beam reflected from the optical card 8 is brought to an optical beam designated as the optical axis 18b and forms a faded spot having its center at a position designated as 19b on the photo detector 10. The output signal from the four-divided light receiving device 20 have the relationship of (A+B)-(C+D)&gt;0. Accordingly, a value (A+B)-(C+D) derived from the output signals from the four-divided light receiving device 20 on the optical detector 10 becomes a focus error signal.
A method of detecting a tracking error will be described next. As shown in FIG. 2, two primary diffracted optical beam spots 15 and 16 are respectively located such that a part of each overlaps one of track guides 11. Under a condition in which there is no tracking error, equal positions of the respective spots 15 and 16 of the primary diffracted beams overlap the track guides 11. Accordingly, the quantities reflected from the track and track guides at the spots 15 and 16 respectively are equal to each other. Thus, an output signal from the light receiving element 21 of E shown in FIG. 3(b) and an output signal from the light receiving element 22 of F have the relationship of E-F=0.
On the other hand, when a tracking error is generated, the overlapping portions of the respective spots 15 and 16 on the track guide 11 become different in size from each other. Thus, the quantity of light reflected from the track and track guide at the spot 15 and the quantity of light reflected at the spot 16 are different from each other due to a difference in the reflectance of the track guide 11 and the reflectance of an information recording track 12.
For the reason discussed above, the output signal from the light receiving element 21 of E and the output signal from the light receiving element 22 of F have the relationship of E-F&gt;0 or E-F&lt;0, depending upon the direction in which the track shifts. Accordingly, a value (E-F) namely, the distance between the value of the output signal from the light receiving element 21 and the output signal from the light receiving element 22 on the photo detector 10 are computed and become the tracking error signal.
As discussed above, under a condition in which there is no focus error and no tracking error, the photo detector 10 is adjusted such that the focus error signal and the tracking error signal are both brought to zero with respect to the three optical beams, so that detection of focus error and tracking error can be accurately executed. Accordingly, when the objective lens is feedback-controlled along the focus direction and along the tracking direction on the basis of the detected signal, the optical beam comprised of zero-order diffracted light is always accurately focussed so as to create an optical beam spot 14 on the optical card and, simultaneously, is so controlled as to be positioned at the center of the information recording track 12, as shown in FIG. 2.
Accordingly, upon recording, a plurality of pits 13 can be formed accurately on the information recording track 12 by the optical beam spot 14 of the zero-order diffracted light modulated on the basis of information to be recorded. Upon playback, a change in the quantity of light reflected from the spot 14 due to the pits 13 on the information recording track 12 is detected by the sum (A+B+C+D) of the output signals from the four-divided light receiving device 20 on the optical detector 10 shown in FIG. 3(b). Thus, it is possible to accurately play back the information recorded on the recording medium.
However, in the optical head of the prior art example, the light receiving elements on the optical detector are formed beforehand into a requisite pattern by a semiconductor process. Accordingly, upon regulation of the position of the light receiving element with respect to the optical beam, it has been required that the entire photo detector be moved with an accuracy of from a few microns to several tens of microns by a jig or the like provided separately, and the photo detector is fixed by means of screws or the like so that a shift in position does not occur. For this reason, there are problems that skillful technique is required for this regulating operation, shift in position is apt to occur at fixing so that time of re-regulation is required abundantly, and the like.
On the other hand, an optical head apparatus is disclosed in Japanese Patent Laid-Open No. 63-824 (824/1988) wherein, as shown in FIG. 4, an optical detector 25 is used, and wherein a plurality of light receiving elements S11 to S1010 are formed in a matrix arranged so as to dispense with mechanical focus regulation. In this optical head apparatus, the optical detector 25 illustrated in FIG. 4 is used to execute focus control by, for example, an astigmatism method. Light receiving elements (represented by Sa, Sb, Sc and Sd, respectively) belonging respectively to four regions Da, Db, Dc and Dd divided by an Xo axis and a Yo axis set provisionally are read. The Xo axis is set to one of the positions from X1 to X11, and the Yo axis is set to one of the positions from Y1 to Y11 such that the sum of the outputs from the light receiving elements belonging to the regions Da, Db, Dc and Dd (represented by Sa, Sb, Sc and Sd, respectively) achieves to the following relationship: EQU (Sa+Sb)-(Sc+Sd)=0 EQU (Sa+Sc)-(Sb+Sd)=0
After the setting of the Xo axis and the Yo axis, a difference between sum of the outputs of the regions Da and Dc diagonally opposite to one another and the sum of the outputs of diagonally opposite regions Db and Dd, that is, (Sa+Sc)-(Sb+Sd) is used for focus-control as a focus error signal.
In this prior art example, the optical detector 25 is not referred to as an image sensor of X-Y address type. Accordingly, it is considered that all the light receiving elements, that is, S11 to S1O1O must be read in order to produce a single focus error signal. For this reason, it takes a lot of time to produce a single focus error signal. Further, nothing is suggested nor referred to in the prior art example, regarding the fact that the tracking error signal is produced by the optical detector 25. Moreover, nothing is suggested nor referred to in the prior art example, regarding the fact that a playback signal is produced by the optical detector 25.